Brain damage and death are direct consequences of prolonged apnea, particularly when combined with hypoxia. The problem of hypoxia and apnea are particularly troublesome when a patient is sedated, as is the case in many medical procedures. Diagnosing hypoventilation and apnea by detecting reduced breathing frequency or breath volume (known as tidal volume) may prompt an early intervention to stimulate breathing, relieve airway obstruction, and restore effective respiration. It is safer to detect inadequate or absent respiration early and restore respiration to normal before hypoxia occurs, than to have a patient suffer from hypoxic-ischemic brain damage.
Two important components of gas exchange in the lungs are oxygenation and ventilation. Oxygenation is commonly monitored non-invasively using pulse oximetry. In contrast, ventilation can only be monitored continuously and non-invasively by measuring the carbon dioxide partial pressure in the exhaled breath. However, there are no inexpensive carbon dioxide detectors that are portable (i.e., can be lifted by a human with a single hand without the aid of a machine).
Ventilation may be measured by examining movement of the chest and ribcage using sophisticated monitors, such as those used in sleep studies. However, these monitors are expensive, cumbersome, non-transportable, and therefore are limited to use in a laboratory.
Currently, there are no devices that provide a non-invasive, portable and semi-quantifiable measure of ventilation in individuals whose airways are not instrumented. Such a device would be useful to detect breathing and measure respiratory rate, and would be particularly useful to detect inadequate respiration or apnea during and after sedation, and general and regional anesthesia, and in those in whom unexpected breathing obstruction (i.e., obstructive sleep apnea, Ondine's curse) or sudden respiratory arrest (i.e., after cleft palate surgery) may occur.